Reflective spatial light modulators (SLM) have been utilized due to the high speed output thereof. As processing techniques improve, the ability to manufacture small SLM arrays has increased. However, one disadvantage to the smaller arrays is that the irregularities in the surface utilized to create the reflective surface under the liquid crystal element becomes important.
In the construction of the reflective SLM, a semiconductor substrate is typically utilized to provide a control surface over which is formed an array of mirror elements, which mirror elements provide both a reflective surface and an electrical control for the liquid crystal. The liquid crystal is then disposed above the substrate with a transparent electrode disposed on the opposite side thereof. This provides for full control of the liquid crystal.
When light impinges upon the upper surface of the liquid crystal, it is transmitted therethrough to reflect off the upper mirrored surface of substrate. Depending upon the electrical characteristics of a particular mirrored element on the surface of the substrate, a phase shift of the light passing therethrough will result. External polarizing elements provide for selectivity of this light, which is conventional. When fabricating the substrate, an array of transistors or control elements are integrally fabricated on the substrate and then various layers of insulting material, conducting strips and possibly metal layers are disposed on the substrate above the active components to provide an interconnecting control network. This interconnecting network is fabricated from a number of processes involving multiple deposition, patterning and etching steps. This typically results in a very irregular surface relative to the wavelengths of light utilized in SLM applications. As dimensions of each of the mirrored elements in the array on the surface of the substrate decreases, this irregularity will be reflected in the contour of the mirrored element and will result in scattering of light. This will reduce the amount of light reflected in the direction of interest and, therefore, the brightness as perceived by the viewer.